1. Field of the Invention
This invention relates to an ultrafine particle enclosing fullerene produced by a novel method and a production method thereof.
2. Description of the Related Art
Fullerene representative of C.sub.60 is bonded with intermolecular forces, and is a football-like molecule having highly symmetrical configuration. All carbon atoms in the molecular are equivalent, and are bonded by a covalent bond. Therefore, the fullerene is an extremely stable crystal. The fullerene like C.sub.60 gather to form the fcc (face-centered cubic lattice) crystallographic structure assuming it as a large atom, and shows metallic mechanical properties such as a plastic deformation capability, a work hardening, or the like. Consequently, the fullerene is expected to be applied for various uses as a new carbon material. Furthermore, applications of the fullerene for a superconductor material, a catalyst, a nonlinear optical material, or the like are studied based upon the properties of the fullerene itself.
Conventionally, the fullerene like C.sub.60 is produced by an arc discharge method using a carbon rod or a granular carbon as an electrode, or a laser ablation method irradiating an ultraviolet laser on a graphite surface. The fullerene is produced in a mixed state in a carbon soot, and is extracted by a collector using a filter or benzene.
Higher-order fullerenes (giant fullerenes) called a carbon nanocapsule or a carbon nanotube are included in a soot deposited on the cathode in the above-mentioned arc-discharge. By pulverizing the deposit on the cathode, and then refining pulverized substances using an organic solvents such as ethanol, the above-mentioned carbon nanocapsules or carbon nanotubes are obtained. Since both the carbon nanocapsules and the carbon nanotubes have a hollow shape and an excellent lubricity and weathering resistance, synthesis of new substances and search for new functionalities are pursued by caging metal atoms, fine crystals, or the like in the hollow portions.
The fullerenes are reported hitherto involving a carbide of rare earths such as La, Y, or the like, and metal fine particles such as Fe, Co, Ni, or the like, as a fullerene caged other metal atoms, fine crystals or the like in the hollow portion of the carbon nanocapsule or the carbon nanotube mentioned above (referred to as an enclosing fullerene). These are obtained by the arc-discharging, or the like using a carbon electrode included a powder of metal, oxide, or the like, and by refining the enclosing fullerene included in the deposit on the cathode. However, the conventional production method for the enclosing fullerene has complex processes. In addition, it is difficult to separate the enclosing fullerene from impurities such as a graphite-like substance, an amorphous carbon, or the like.
Furthermore, as the giant fullerene, onion-like graphite is found where fullerenes having larger molecular weight are layered in a form of concentric circles surrounding a shell of core composed of C.sub.60. However, only a presence of the onion-like graphite is identified, its shape and physical properties are not controlled sufficiently, much less the enclosing fullerene using the onion-like graphite is not realized.
As described above, the conventional enclosing fullerene is included in the deposit on the cathode obtained by the arc-discharge or the like using the carbon electrode included a powder of metal, oxide, or the like. Thereby, the production processes are complex, and separation from impurities such as the graphite-like substance, the amorphous carbon, or the like is difficult.
Therefore, producing the enclosing fullerene with a relative simple process requiring no separation process is needed. Moreover, a technique producing the enclosing fullerene independently under controlled conditions is needed to produce various types of enclosing fullerenes, for example, to easily find a substance capable of involving inside the fullerene, and to grasp, operate, and control physical properties of the fullerene.